1. Field of the Invention
The present invention relates to a pivot assembly bearing device that prevents diffusion of oil and a magnetic head actuator using the same.
2. Description of Related Art
In a magnetic head actuator for use in a hard disk device or the like, conventionally, a swing arm on which a magnetic head that reads and writes a data is supported by a pivot assembly bearing device including a pair of ball bearings. In the pivot assembly bearing device, lubricant sealed inside the ball bearings is prevented from splashing, leaking out or evaporating in order to avoid contamination or damage of a magnetic disk.
Along with an increase in the capacity of hard disk devices in recent years, the gap between the magnetic head of the magnetic head actuator and the magnetic disk is becoming smaller. Therefore, there is an increasing demand to prevent leakage of lubricant sealed in ball bearings of the pivot assembly bearing device.
Material showing prior art that addresses such a demand can be found in Japanese Patent Application Publication No. 11-166526 (JP 11-166526 A) and Japanese Patent Application Publication No. 58-220275 (JP 58-220275 A).
As a rolling bearing device with two ball bearings, JP 11-166526 A discloses a rolling bearing device for a swing arm (pivot assembly bearing device) including a shield plate on at least one of the axially outer sides of the ball bearings for reducing splashing and leaking out of lubricant.
According to the document, it is possible to provide a swing arm rolling bearing device in which splashing and leaking out of lubricant is reduced.
JP 58-220275 A describes a magnetic head actuator including bearings disposed in an air-tight chamber formed by a magnetic fluid seal, in which evaporating lubricating oil (evaporating oil) coming from the inside of the bearings is hindered from adhering to a magnetic disk.
That is, as illustrated in FIGS. 3 and 4 of JP 58-220275 A, a seal main body of the magnetic fluid seal which surrounds a rotary shaft is disposed between the bearing and a rotator. This seal main body includes a hollow cylindrical base body and two annular end plates attached to both end surfaces of the base body. The inner peripheral edge of the end plate is provided in proximity to the outer periphery of the rotary shaft. A colloidal magnetic fluid obtained by stably dispersing ferromagnetic fine powder in an oil-based solvent is supplied between the inner peripheral edge of the end plate and the outer periphery of the rotary shaft. The magnetic fluid adheres to both the inner peripheral edge of the end plate and the outer periphery of the rotary shaft to completely seal the gap between the end plate and the rotary shaft.
According to this document, it is possible to prevent leakage of lubricant due to evaporation of lubricating oil from the inside of the bearing, and to prevent adhesion of evaporating oil to the magnetic disk. Accordingly, the magnetic head becomes operable in a good condition at all times.
However, in the art described in JP 11-166526 A, since there is a gap between the shield plate and the inner peripheral surface of the sleeve, it is difficult to prevent diffusion of evaporating oil from the gap, and to effectively prevent diffusion of evaporating oil from the inside of the bearing.
In the art described in JP 58-220275 A, the magnetic fluid adheres to both the inner peripheral edge of the end plate and the outer peripheral surface of the rotary shaft in order to seal the gap between the end plate and the rotary shaft. Thus, it is possible to prevent diffusion of evaporating lubricating oil (evaporating oil) from the inside of the bearing. However, it is difficult to effectively prevent generation and diffusion of evaporating oil originating from the magnetic fluid provided outside the bearing. Eventually, this makes difficult to prevent adhesion of evaporating oil to the magnetic disk.
In the art described in JP 58-220275 A, a bearing is disposed in an air-tight chamber for which a magnetic fluid is used to prevent diffusion of evaporating oil from the inside of the bearing. However, evaporating oil may be generated and diffused from the magnetic fluid. In addition, the colloidal magnetic fluid may increase torque of the bearing device thereby reducing the response performance of the magnetic head. Therefore, the device is not so useful in preventing adhesion of evaporating oil to a magnetic disk. Thus, it has been desired to develop a rolling bearing device for swing arm capable of preventing generation and diffusion of evaporating oil without using a magnetic fluid outside a bearing, that is, without disposing a bearing in an air-tight chamber.